Field of the Invention
The invention relates to a device for using endoscopy to search for defects on parts that are masked, i.e. that are not directly visible, e.g. such as parts inside a turbine engine.
Description of the Related Art
It is known to inspect the internal components of equipment or of a machine with the help of an endoscope which is an elongate optical instrument of small diameter that is passed through a small orifice in a wall in order to examine the appearance of components that are to be found on the other side of the wall. The endoscope can thus be used for inspecting blades of a turbine engine such as an airplane turboprop or turbojet without it being necessary to disassemble the engine.
In order to view defects of a part, it is known to use a penetrant test technique that consists in depositing organic materials on the surface under examination of the part and in observing under ultraviolet illumination the extent to which the organic materials impregnate the surface of the part. The presence of defects is revealed after drying the surface of the part and depositing a developer material that reveals the organic material that has infiltrated into surface defects of the part when the part is illuminated with ultraviolet light.
In order to facilitate the use of the penetrant testing technique on an airplane engine while it is attached under the wing of an airplane, proposals have already been made in document U.S. Pat. No. 4,273,110 to use an endoscope incorporating penetrant test means. For that purpose, the proposed instrument comprises an elongate rigid cylindrical sheath of small diameter containing a duct that is used for passing means for guiding ultraviolet light and visible light towards an end of the instrument that is close to the part for inspection. The instrument also has an optical duct for integrating means for transmitting and forming images in order to observe the illuminated zone, and a plurality of ducts, each used for passing a respective penetrant test material.
That type of instrument is relatively easy to use when it is desired to examine a masked part, i.e. a part that is not directly visible and that is situated behind a wall. For that purpose, it suffices to insert the rigid sheath through an orifice in the wall and to perform the inspection in the manner described above. The Applicant has also made proposals in a prior application FR 2 857 094 to perform the penetrant testing and the observation with the help of two separate endoscopes. In another prior application, FR 2 861 185, the Applicant proposes using an endoscope with ultraviolet illumination and deflected distal viewing, the endoscope having a rigid tubular body.
Nevertheless, those prior devices require a plurality of independent ducts for passing different penetrant test materials, thereby requiring the endoscope to have a section that is large and restricting its use to orifices or passages that are sufficiently large.